TM 55-6610-247-40
Table 3-1. Altitude Pressure Table, Feet VS Inches of Mercury (Cont)
PRESSURE INCHES
0.00
0.01
0.02
0.03 0.04
0.05 0.0O
0.07
0.08
0.09
29.9 ..............
20
10 __+1
__8 __17
__2 __36 __45 __54
__63
30.0 ..............
__73 __82 __91 __100 __110 __119 __128 __137 __146
__156
30.1 ..............
__165 __174 __183 __192 __202 __211 __220 __229 __238
__248
30.2 ..............
__257 __266 __275 __284 __293 __303 __312 __321 __330
__339
30.3 ..............
__348 __358 __367 __376 __385 __394 __403 __412 __421
__431
30.4 ..............
__440 __449 __458 __467 __476 __485 __494 __504 __513
__522
30.5 ..............
__531 __540 __549 __558 __567 __57o __585 __594 __604
__613
30.6 ..............
__622 __631 __640 __649 __658 __667 __676 __685 __694
__703
30.7 ..............
__712 __721 __730 __740 __749 __758 __767 __776 __785
__794
30.8 ..............
__803 __812 __821 __830 __839 __848 __857 __866 __875
__844
30.9 ..............
__893 __902 __911 __920 __929 __938 __947 __956 __965
__974
31.0 ..............
__983 __992 __1001 __1010 __1019 __1028 __1037 __1046 __1055
__106
is at the 35,000foot reading, the hysteresis test shall
3-6. Scale Error Test.
commence. Pressure shall be increased at a rate
Scale error test at room temperature of 25C (77F) is as
simulating a descent in altitude at a rate of 5,000 to
follows:
20,000 feet per minute until within 3,000 feet of 18,000
a. Set zero setting system for standard sea level
feet. The test point will then be approached at a rate of
pressure (barometric dial 29.92). Record the reading in
approximately 3,000 feet per minute. The altimeter will be
feet shown by the pointers (this reading will be used for
kept at the 18,000foot pressure for at least 5 minutes but
an aftereffect check). Place instrument in an altitude
not more than 15 minutes before a test reading is taken.
chamber which is connected to a barometer and source
The pressure shall then be increased further, in the same
of suction and pressure.
manner as before, until a 14,000foot pressure is
b. If barometer indicates more than 29.92 inches
reached. The altimeter shall be kept at this pressure for
of mercury, close chamber and reduce pressure until
at least one minute but not more than 10 minutes before
barometer indicates 0 altitude. Note position of pointers
a test reading is taken. The pressure will then be
of test instrument and if pointers are not on 0, open
increased, in the same manner as before, until
chamber to atmosphere and turn adjustment knob to
atmospheric pressure is reached. Neither of the two
reposition pointers. Repeat procedure until pointers of
recorded readings shall differ from the corresponding
instrument indicate 0, simultaneously with indication of
reading during scale error test by more than 120feet. Not
29.92 inches of mercury or barometer.
more than five minutes after reaching atmospheric
c. Subject altimeter successively to pressures
pressure, the aftereffect error shall be recorded. Error
indicated with an asterisk (*) in table 3-2 at a rate of
shall not exceed 30 feet. Allowance must be made for
change in pressure of approximately 3,000 feet per
change in local barometric pressure for aftereffect check.
minute. The altimeter shall remain at pressure
Refer to table 3-3.
corresponding to each test point for I minute before a test
reading is taken except as noted for hysteresis an(d
First Check Point
18,000
379.4 MM
aftereffect test. Scale error shall not exceed tolerances
Second Check Point
14,000
446.4 MM
specified in table 3-2. Do not change the 35,000 foot
scale error pressure before starting the hysteresis check.
NOTE
hysteresis and aftereffect test shall be performed with
Equipment must be leak-proof during
this test. If instrument fails to meet this test, it must be
the test.
readjusted.
3-7. Hysteresis and After-effect Test.
b. If instrument fails to meet this test. trouble
This test must be performed with scale error test
may be corrected by decreasing tension on balance arm.
described in paragraph 3-6.
Adjustments on balance arm are very critical as a change
a. Keeping vibrator on, the hysteresis test shall
of balance tension will affect static balance as well as
begin not more than 15 minutes after the initial exposure
adjustment; therefore, only very minor adjustments
of the altimeter to the 35,000foot pressure of the scale
should be made. A misaligned link on balance arm may
error test. While the altimeter
also cause an apparent hysteresis error. If error cannot
be
Change 6 3-2
